Controlling surface roughness during forging is a complex challenge. Below, we will explain it in detail:

1. Optimizing Raw Material Surface Quality

1) Remove defects from the billet surface before forging: oxide scale, cracks, scratches, decarburized layers, etc., which can be removed by shot peening, turning, grinding, or pickling.

2) Control the surface roughness of the original billet; deep scratches on the raw material will be inherited and amplified after hot deformation.

3) Avoid rust and thick oxide layers on the billet surface before heating.

2. Controlling the Heating Process and Reducing High-Temperature Oxidation

1) Oxide scale is the main cause of surface roughness during hot forging.

2) Use rapid heating to shorten the high-temperature holding time.

3) Use a protective atmosphere furnace, inert gas protection, or apply an anti-oxidation coating to the billet to inhibit oxide scale formation.

4) Avoid overheating and burning of the workpiece.

5) Remove the formed oxide scale immediately before forging (air blowing, water washing, mechanical descaling). 

3. Improve Die Surface Condition

1) Maintain a smooth forging die surface: Regularly grind and polish the die cavity. Any pits, wear marks, and corrosion on the die will transfer to the forging.

2) Repair die surface wear, thermal fatigue cracks, and scratches promptly.

3) Reduce die sticking (workpiece adhering to the die), which can lead to material tearing and surface unevenness.

4. Proper Selection and Use of Lubricants

Lubricants form a separation film between the workpiece and the die:

1) Select suitable forging lubricants: graphite-based lubricants, glass-based lubricants (for high-temperature alloy forging), polymer lubricants.

2) Ensure a uniform and moderate lubricant coating; excessive lubricant can lead to buildup and surface pitting; insufficient lubrication can cause metal sticking and scratches.

3) Prevent lubricant carbonization and residue buildup within the die cavity. 

5. Controlling Forging Operations and Eliminating Forming Defects

1) Avoid metal folding, overlapping, and underfilling during the forming process, as these will cause severe surface irregularities.

2) Ensure proper die closure to avoid flash defects caused by improper billet positioning.

3) Regularly clean the die cavity to remove oxide scale, lubricant residue, and metal debris.

6. Post-Forging Treatment

1) Use controlled cooling to avoid secondary oxidation after forging.

2) If stricter surface roughness requirements are needed, post-treatments such as shot peening, tumbling, or grinding can be performed.